Typing for rules created in parser constructor

[khkiley]

When creating a parser class by extending the parser, the rules are created in the constructor.

    this.RULE('numericExpression', () => {

    ......

    });

And then later on when consuming the subrule:

    $.RULE('parenthesisExpression', () => {

        $.CONSUME(OpenParen);
        $.SUBRULE($.numericExpression);
        $.CONSUME(CloseParen);

    });

Which results in a Typescript error on $.SUBRULE($.numericExpression) because 'numericExpression' does not exist on the new parser.

How are others addressing this ?

Thanks,

Kurt

[msujew]

Hey @khkiley,

I cannot really follow. Can you give a reproducible example?

[khkiley]

Thanks for the superfast reply!

Maybe a screenshot from VSCode will be clearer:

Those red squiggles under the rules are type errors, indicating the rule is not defined on the class.

[msujew]

Oh, I see that's what you mean. For TypeScript, you need to perform the assignments manually for the compiler to pick it up. Instead of performing the RULE calls inside of the constructor, you can also move them outside of it:

class SomeParser extends EmbeddedActionsParser {
  constructor() {
    super(tokens, {
      recoveryEnabled: true
    });
    this.performSelfAnalysis();
  }
  
  private numericExpression = this.RULE(...);
  private expression = this.RULE('expression', () => {
    ...
    this.SUBRULE(this.numericExpression);
  });
}

[bd82]

There is an example for this here:

• https://github.com/Chevrotain/chevrotain/blob/master/examples/implementation_languages/typescript/typescript_json.ts

[khkiley]

Oh, perfect! I was unaware that this could work.

Thank you.